Field of the Invention
The present invention relates to an explosion-proof valve and a manufacturing method thereof. The explosion-proof valve according to the present invention is installed, for example, to a sealing plate of a capacitor, or installed to various batteries such as a secondary battery.
Description of the Conventional Art
As an explosion-proof valve installed to a pressure vessel for a capacitor and various batteries, there has conventionally known an explosion-proof valve 61 of a type that is installed to a hole portion 52 of a pressure vessel 51 from an outer side (an upper side in the drawing) of the pressure vessel 51. In a structure of the explosion-proof valve 61, a tubular portion 62 inserted to the hole portion 52 is provided, an outside flange portion 63 is provided in one end portion (an outside end portion of the vessel, an upper end portion in the drawing) of the tubular portion 62, a locking projection 64 is provided in the other end portion (an inside end portion of the vessel, a lower end portion in the drawing) of the tubular portion 62, and a membrane portion 65 is provided in an inner peripheral side of the tubular portion 62, the membrane portion 65 valve opening when the pressure (the internal pressure) within the pressure vessel 51 goes beyond a predetermined valve so as to release the pressure (refer to Japanese Unexamined Patent Publication No. 10-050569).
In the explosion-proof valve 61 mentioned above, in order to prevent the explosion-proof valve 61 from separating and detaching from the hole portion 52 of the pressure vessel 51 before the membrane portion 65 ruptures due to rising of the internal pressure, it is necessary to set an outer diameter d3 of the locking projection 64 to be sufficiently greater in relation to an inner diameter d1 of the hole portion 52 (height of the locking projection 64=(d3−d1)/2).
However, in this kind of conventional explosion-proof valve 61, since an outer diameter d4 of the outside flange portion 63 is set to be further greater than the outer diameter d3 of the locking projection 64, the following disadvantage is generated.
More specifically, as shown in FIG. 6A, in the case that the explosion-proof valve 61 is molded by a molding die having a split structure, the explosion-proof valve is molded by using a molding die 71 in which a mold split position 72 in the split structure is arranged at a position of the outside flange portion 63 in the explosion-proof valve 61 in order to reduce forced extraction positions at the mold releasing time as much as possible.
Therefore, in the molding die 71, since the locking projection 64 in the explosion-proof valve 61 is set to the forced extraction position at the mold releasing time as shown in FIG. 6B, the locking projection 64 may be broken at the mold releasing time in the case that the outer diameter d3 of the locking projection 64 is set to be larger as occasion demands (a problem in a valve defective molding)
As a result, conventionally, the outer diameter d3 of the locking projection 64 can not be set to be sufficiently greater. Accordingly, the explosion-proof valve 61 may separate from the hole portion 52 of the pressure device 51 (a problem in a valve detachment).
There can be thought that suppression of defective molding and securement of the outer diameter of the locking projection are achieved by using a molding die having a three-piece split structure (not shown), however, since a die cost is extremely increased in this case, this case can not be an effective countermeasure.